1. Field of the Invention
The present invention relates to an improvement of a sheet discharge part in a sheet processing apparatus used in combination with an image forming apparatus.
2. Description of the Related Art
When delivering sheets on which images are formed or sheets on which images are formed and post processing such as punch processing, binding processing, and punching processing is conducted, to a sheet discharge tray, sorting processing is conducted and delivered.
In the sorting processing, there is a shift processing which is simple and most widely conducted, and this shift processing is a processing in which, for each number of setting sheets, the sheets are displaced in a conveyance width direction, that is, a direction perpendicular to the conveyance direction and parallel to the sheet surface of the conveyed sheet, and discharged.
As the shift processing, a method in which, in the sheet discharge port, the sheet is freely dropped from sheet discharge port and stacked on the sheet discharge tray, is common.
In such a shift sheet discharge, because the sheet is separated from sheet discharge port and freely dropped, the deviation is generated in the movement of the sheet in the process of the drop, and the grounding position on the sheet discharge tray of the sheet, is deviated, and there is a problem that the alignment condition of the sheet on the sheet discharge tray is not so good.
In Japanese Unexamined Patent Application Publication No. 2001-187665 (hereinafter referred to as JPA 2001-187655), in order to solve this problem, it is proposed that an aligning means for guiding the sheet on the stage that the sheet is not separated from the sheet discharge port is used, and the sheet is aligned.
In JPA 2001-187655, in order to shift the sheet, the discharge tray is displaced in the conveyance width direction.
Although the shift processing is not conducted, in Japanese Unexamined Patent Application Publication No. 2003-2524 (hereinafter referred to as JPA 2003-2524), a regulating member which guides the side edge of the sheet on the sheet discharge tray is used.
In JPA 2001-187655 and JPA 2003-2524, when the sheet is placed on the sheet discharge tray, the sheet is guided not by free-dropping, but by regulating member, and stacked.
Then, for the shift processing which changes the sheet position to the conveyance width direction, in JPA 2001-187655, the sheet discharge tray is displaced, and in JPA 2003-2524, it does not have the shift function.
In the shift processing of the JPA 2001-187655, the sheet discharge tray displaces in the conveyance width direction. Therefore, when a lot of sheets are stacked on the sheet discharge tray, because the sheet discharge tray having a large mass reciprocates and the inertia functions, the drive mechanism corresponding to this, is necessary, and a large drive mechanism becomes necessary.
Further, because the stacked sheets repeat the movement in the conveyance width direction, there is a case where the alignment condition is broken.
Further, because the sheet discharge tray moves in the conveyance width direction, when the sheet discharge tray is elevated and lowered, there is a problem that the drive mechanism of the sheet discharge tray becomes complicated.